This section provides background information related to the present disclosure which is not necessarily prior art.
There is proposed a magnetic refrigeration system utilizing a phenomenon (magnetocaloric effect) such that when a magnetic field is applied to a magnetic working material such as a magnetic material, the magnetic working material generates heat and such that when the magnetic field is removed from the magnetic working material, the magnetic working material is decreased in temperature (see, for example, patent document 1).
The magnetic refrigeration system of this patent document 1 is constructed of: a magnetic working material mounted in a railroad vehicle; a strong magnetic field generating device for applying a magnetic field to the magnetic working material; a first heat exchange flow passage through which a heating medium for transferring the heat (hot heat) of the magnetic working material flows, the heat (hot heat) being increased when the magnetic field applied to the magnetic working material by the strong magnetic field generating device is increased; a second heat exchange flow passage through which the heating medium for transferring the heat (cold heat) of the magnetic working material flows, the heat (cold heat) being decreased when the magnetic field applied to the magnetic material by the strong magnetic field generating device is decreased; and pumps and heat exchangers arranged in the respective heat exchange flow passages.
When the magnetic field applied by the strong magnetic field generating device is increased, the pump disposed in the first heat exchange flow passage is activated to make the heating medium whose temperature is increased by the hot heat of the magnetic working material exchange heat with air outside a passenger compartment by the heat exchanger. On the other hand, when the magnetic field applied by the strong magnetic field generating device is decreased, the pump disposed in the second heat exchange flow passage is activated to make the heating medium whose temperature is decreased by the cold heat of the magnetic working material exchange heat with air inside the passenger compartment by the heat exchanger.
By the way, in the magnetic refrigeration system of the patent document 1, the strong magnetic field generating device is constructed of a superconducting coil or the like so as to increase a temperature change in the magnetic working material and the application of the magnetic refrigeration system is limited to special uses. Hence, it is difficult to apply the magnetic refrigeration system to a general-purpose product such as a vehicle air conditioning device.
As a means for solving an issue like this has been known an AMR (Active Magnetic Refrigerator) type magnetic refrigeration system in which: after a magnetic field applied to a magnetic working material is increased, refrigerant (magnetic heat transporting medium) is transferred to one end (high temperature end) in the magnetic working material; and after the magnetic field applied to the magnetic working material is decreased, the refrigerant is transferred to the other end (low temperature end) in the magnetic working material, whereby the cold heat and the hot heat generated by the magnetocaloric effect are stored in the magnetic working material itself.
The AMR type magnetic refrigeration system generally has a container filled with a magnetic working material and having a refrigerant flow passage through which a refrigerant flows and reciprocally transfers the refrigerant between one end and the other end of the container according to applying and removing a magnetic field to and from the magnetic working material.
The following four processes are repeated: (i) applying the magnetic field to the magnetic working material; (ii) transporting hot heat generated in the magnetic working material to the one end (high temperature end) of the container by the refrigerant; (iii) removing the magnetic field from the magnetic working material; and (iv) transporting cold heat generated in the magnetic working material to the other end (low temperature end) of the container by the refrigerant.
In this way, a temperature gradient is produced in the magnetic working material in the container and hence a large temperature difference is produced between a high temperature end and a low temperature end in the container.
Here, it may be thought that the AMR type magnetic refrigeration system is applicable to the magnetic refrigeration system of the patent document 1. However, in this case, there is presented an issue that the COP (Coefficient Of Performance) of refrigeration of the magnetic refrigeration system is reduced. Here, the COP expresses a cooling or heating capacity per 1 kW of power consumption.
This is because a refrigerant flowing through a refrigerant flow passage is made to exchange heat with a heating medium flowing through a heat exchange flow passage, around a magnetic working material, in the case where the AMR type magnetic refrigeration system is applied to the magnetic refrigeration system of the patent document 1. Hence the heat of the magnetic working material is transmitted indirectly to the heating medium flowing through the heat exchange flow passage. At this time, a heat exchange loss is increased between the magnetic working material and the heating medium.